Safety of shell eggs as affected by rate of heating during pasteurization to inactivate Salmonella Enteritidis

Thermal shell egg pasteurization is a technology developed to combat Salmonella contamination. The process includes three steps: come-up, holding and cooling. We hypothesize that slow heating rate during come-up stage, as practiced commercially, could trigger adaptive heat stress response in Salmonella which may compromise product safety.
The objectives of this study are to understand how different heating rates during come-up stage could affect (1) the expression of heat-stress-response related genes, (2) Salmonella heat resistance during holding stage and Salmonella recovery during cooling stage, and (3) expression of Salmonella virulence genes.
In objective 1 and 3, transcriptomic analysis was conducted to determine the expression level of heat-stress-response and virulence genes. Compared to fast heating rate, slow rate caused higher expression of heat resistant genes. The expression of virulence in response to heating rate varied by genes.
In objective 2, D values at holding temperature 53°C were measured. D53°C measured following fast heating rate was significantly shorter than that following slow heating rate (D53°C of 8.9±1.6 vs. 14.4±1.3min). Salmonella population in yolk was monitored during the subsequent 8-h cooling. During the first 30-min of cooling, Salmonella population in eggs processed with fast heating rate decreased by additional 1.3±0.5log whereas no reduction was observed with slow heating rate. However, the overall recovery of Salmonella was 1.7 ±0.4CFU/ml from slow heating rate and 0.4±0.6log CFU, fast heating rate.
Our research suggests that fast heating rate at the processing come-up stage could result in safer pasteurized shell eggs; egg processors should consider the implications.